1. Field of Industrial Utilization
The present invention relates to a shortened non-grounded type ultrashort-wave antenna that is used as a handy type wireless telephone antenna of, for instance, cellular telephone systems.
2. Prior Art
In handy type wireless telephones used in cellular telephone systems, there is an increasing demand for making them compact and light-weight. An improved performance, easy handling, etc. are also demanded along with a novel design.
In the handy type wireless telephone systems, it is necessary to use a non-grounded type antenna or an antenna similar to this type in order to maintain a constant performance level regardless of whether the telephone is in use or not. In addition, since the wireless telephone is an equipment for two-way communication, it is necessary that the antenna can receive all call signals from callers at any time.
In the handy type wireless telephones of earlier days, the antenna element sticks out of the telephone set to secure a minimum reception sensitivity at all times. However, in such a telephone system the antenna element, which has the same length as the height of the wireless telephone set, always sticks out. Such a projected antenna is, however, inconvenient when the telephone is not in use. In particular, it is extremely inconvenient when the telephone set is stored, transported, etc. For example, female users express dissatisfaction because they cannot put the wireless telephone set in their handbags due to the antenna element that is fixed projected. There are many other complaints.
In view of the above, it is desirable that a wireless telephone that has an antenna element which retracts inside the telephone set. The problems described above are indeed eliminated if an antenna is retractable. However, if the design change is only to make the antenna element retractable inside the wireless telephone set, there is naturally a severe drop in the gain, directionality and impedance of the antenna which are the three most important factors in the antenna function. As a result, call signals from callers cannot be received. In addition, since the antenna element must be extended when it is used and then retracted after the use, handling of the telephone set becomes more complicated. As a result, the "convenience" of the wireless telephone tends to be diminished.
Historically, the use of retractable antenna elements of the type described above has long been known. One well known antenna is an externally attached, shortened grounded type antenna having the length of .lambda./4. This antenna is obtained by shortening the overall length of the antenna element. The antenna requires no extension or retraction features and is mounted on a wireless telephone case; therefore, it has attracted a great deal of attention because it satisfies the demands described above. In other words, since there is no need to extend or retract the antenna element, handling of the antenna of is easy. In addition, since the length of the antenna element projecting from the case is extremely short, the antenna does not involve any inconvenience when the telephone is not in use, resulting in that the telephone set can fit into any handbag relatively easily.